This invention relates to a method for shearing a wavefront of an object under test by using two holograms as the interferometer and to a shearing interferometer to be used for effecting said method.
Heretofore, such devices as the Ronchi-grating and the Mach-Zehnder interferometer have generally been adopted for the determination of lens aberration, distribution of refractive index in glass plates, distribution of refractive index in fluids, and so on. With the Ronchi-grating, since the maximum available area for producing the interference patterns is 50%, the field of vision is narrow, the contrast of produced interference fringe is not sharp and the degree of shearing cannot be varied. The Mach-Zehnder interferometer is deficient in optical stability and is complicated in adjustment because it is not a common path type instrument.
The hologram has to date been employed generally as a medium for recording. In the conventional shearing interferometry using the hologram, therefore, it has been necessary to use a complicated optical system because the interference fringe of a wavefront from an object under test has been recorded on an individual basis on each hologram. By this method of shearing interferometry, it is difficult to carry out the desired measurement easily at a desired place. Further, since this method inevitably requires the photographic plate containing the recorded image to be developed, it does not permit real-time observation of shearing interferometry.
An object of this invention is to provide a shearing interference which provides the desired amount of shear of the interference fringe of an object with extreme ease at any desired place.
Another object of the present invention is to provide a shearing interferometer which permits ready variation of the amount of shear and which enables the shearing of the interference fringe to be obtained with high accuracy.